This invention relates to a radiation detector used for an X-ray CT scanner system, and more particularly to a multi-element type radiation detector which has less variation of detection sensitivity due to the position of incidence of radiation and variance of sensitivity between individual elements but has high detection sensitivity.
A large number (e.g. 512 ch.) of elements are used in the X-ray CT scanner system. If sensitivity variance exists between these elements, round artifact develops on a reproduced image. Accordingly, uniformity of sensitivity between the elements is of utmost importance. Sensitivity distribution inside each element is also an important factor which determines discrimination capacity or resolution on the image.
As an example of radiation detectors for such an X-ray CT scanner system, Japanese Patent Laid-Open No. 24174/1987 discloses a structure wherein silicon photo-diodes are bonded by a bonding material on the surface of a scintillator opposite to the surface of incidence of X-rays. However, the X-ray detector using the bonding material involves the following problems:
1. A position error occurs between the scintillator and the photo-diode when they are bonded, and sensitivity variance inside the element occurs, too.
2. High level of skill and labor are necessary in order to bond precisely the scintillator and the photo-diode for a large number of elements.
3. An extremely high level of technique is necessary to arrange a large number of elements in intimate contact with one another and with high position accuracy.
On the other hand, Japanese Patent Laid-Open No. 71881/1987 discloses a structure wherein an amorphous silicon layer is formed on the surface of the scintillator and is used to form photo-diodes, in place of coupling of the scintillator and the photo-diode by use of the bonding material. According to this structure, an optical coupling state between the scintillator and the photo-diode is extremely stable and sensitivity variance resulting from the bonding material decreases. However, since this prior art technique fabricates a multi-element X-ray detector for an X-ray CT scanner system by arranging a large number of laminate structures each consisting of the scintillator and the photo-diode and being formed individually, a great deal of labor is necessary for accurately arranging a large number of elements. Furthermore, a signal line must be wired to each element so that an extremely high cost is necessary for apparatuses in order to prevent all of these wirings from generating noise due to mechanical vibration.